Strain ageing in γ(TiAl)-based titanium aluminides due to antisite atoms

Abstract The deformation behaviour of two-phase titanium aluminides was investigated in the intermediate temperature interval 450–750 K. The observed deformation characteristics include discontinuous yielding and negative strain rate sensitivity, which are indicative of the operation of the Portevin–LeChatelier effect. The pinning processes occurring at the dislocations and associated with these phenomena were studied by static strain ageing experiments. A wide range of alloy compositions and microstructures was investigated in order to identify the relevant defect species. Accordingly, dislocation pinning is characterized by a relatively small activation energy of Q a =0.7eV being not consistent with a conventional diffusion process. Furthermore, the strain ageing phenomena are most pronounced in Ti-rich alloys. This gives rise to the conclusion that antisite defects are involved in the pinning process.